Brake pressure control apparatus

ABSTRACT

A brake pressure control system for automotive vehicles with an anti-locking control system is disclosed, in which an outlet valve (10) associated with a wheel cylinder has a closing element (5) which is coupled to the closing element (6) of the inlet valve (11) through a coupling housing (14) so that the closing element (5) of said outlet valve opens the closing element (6) of the inlet valve (11) and in its open position it allows closing of the closing element of the inlet valve. A plurality of valve chambers and the action of a self regulating a control bushing (48) which also acts as the coupling, a flow limiting valving action to the wheel cylinder (2) is attained. In another embodiment, inlet and outlet solenoid valves are operated by a single common electrical line, the inlet valve held closed despite deenergization by inlet fluid pressure from the master cylinder or pump as long as the pressure therefrom is greater than the pressure in the wheel cylinder.

BACKGROUND OF THE INVENTION

The invention is related to a brake pressure control system, inparticular for automotive vehicles, with an anti-locking control (ABS)and/or with a traction slip control (TSS), which operates with hydraulicfluid pressure, such systems include a master cylinder, one or morewheel cylinders for wheel brakes, and a pressure modulator for themodulation of the hydraulic pressure within said wheel cylinders of thewheel brakes in the course of a brake pressure control mode. Thesesystems also include a motor-driven pump for the generation of hydraulicpressure, and an electronic controller, and an inlet and an outlet valveassociated with each wheel cylinder.

An example of such a brake system is described, for example, in theGerman patent application published without examination, No. 3,731,603.The application of the invention is, however, not limited to this type.

The electronic controller controls operation of the inlet and outletvalves in accordance with the control algorithm incorporated in thecontroller. A pressure reduction phase is generated in the wheelcylinder when the outlet valve is open and the inlet valve is closed.When the inlet valve is closed and the outlet valve is closed, apressure stabilization phase is established, and, when the inlet valveis open and the outlet valve is closed a pressure rebuilding-up phaseensues.

Furthermore, hydraulic connections have been described in which theinlet valve has a restriction effect. Please refer to the German patentapplication No. P 3,919,842.1 in this respect.

In that patent application, a hydraulic brake system for a vehicle isdescribed which is equipped with an anti-locking control system and iscomprised of a master cylinder, a fluid pressure accumulator, at leastone wheel brake which is in connection with the master brake cylinderthrough a brake line and is in connection with the fluid pressureaccumulator through a return line. An electromagnetically actuatedoutlet valve is inserted in the return line and shuts off the returnline in its normal position and opens the return line in its switchingposition. A restriction valve is incorporated in the brake line,furnished with two switching positions, an unrestricted connectionexisting between the wheel brake and the master brake cylinder in thefirst switching position and a restricted connection existing betweenthe wheel brake and the master brake cylinder in the second switchingposition. A pump aspirates fluid under pressure from the fluid pressureaccumulator and delivers it through a pressure line into the mastercylinder. A sensor monitors the angular velocity of the wheel to bebraked, and an electronic evaluation unit evaluates the sensor signaland generates switching signals for the pump drive and for the outletvalve.

It is proposed in the forementioned German patent application that therestriction valve is connected by means of a control line to the outletof the pump so that the pressure at the outlet of the pump puts therestriction valve from the first into the second switching position.

See the above-mentioned German patent application No. P 3,919,842.1 foran illustration of this type of system.

See also U.S. Pat. No. 4,090,739 which describes another such system.

A brake system with anti-locking control is described there which issuited for use in motorcycles or in small automotive vehicles. Thesystem is comprised of an electromagnetically actuatable anti-lockingcontrol. valve which may assume different positions: a normal position,a pressure decreasing position and a locking position between twopistons. The valve is subject to the action of a spring, urged to thenormal position. In that position, the valve communicates brake pressureto the wheel cylinder. In the anti-locking control mode, the valve isslid into the pressure decreasing position. The valve is hindered fromreturning from the pressure decreasing position into the normal positionas long as fluid pressure is exerted by the master cylinder. The valveremains in the locking position when the supply of fluid pressure islocked. A bypass is provided which bridges the control valve. Arestricted cross-sectional area of flow is envisaged in the bypass. Theobjective achieved is that in a second and subsequent pressure build-upphases only a limited volume of brake fluid is made available.

Further details may be seen in the above-mentioned U.S. patent.

The present invention has the following objects:

Basically, the cost of manufacture is to be reduced. This is to beachieved in particular by the saving of magnet coils, of electricallines and of plug pins.

The assembly space required for the incorporation of the anti-lockingcontrol is to be reduced.

The applicability of the inventive anti-locking control is to be moreuniversal than customary according to the state of the art. For example,an application for so-called "open" and "closed" brake systems withanti-locking control is to be possible. Open brake systems are thosesystems in which a fluid reservoir is vented to the atmosphere andclosed systems are systems which do not have an unpressurized reservoir,

The present invention allows the brake passive control to be integratedin the valve block of the control unit.

By the present invention attaining the effect of a flow limiting valveis enabled. This means that after reaching a nominal flow rate, thisflow rate is maintained substantially constant notwithstandingfluctuations of the pressure level or pressure differentials upstreamand downstream of the valve.

"Nominal flow rate" means in this case that not more than a definedvolume of fluid per unit of time is conveyed to the wheel cylinder inthe anti-locking control mode, regardless of the level of the pressureon the delivery side of the pump or the pressure side of the mastercylinder.

It is, moreover, part of the object of the invention that besidesavoiding undesirably high wheel cylinder pressures in the control mode,a rapid pressure reduction takes place in the control mode when apressure reduction is prescribed by the control algorithm. The controlquality is to be improved generally.

The invention has, furthermore, the object to eliminate theelectromagnetically actuated inlet valves, open when deenergized, whichare typically required in the prior art.

Furthermore, the invention should allow this control independent of anychanges of the viscosity and temperature of the fluid. Constant pressuregradients during control should be enabled by the invention.

It is, moreover, one of the objects of the invention to reduce or toprevent any noises during the control mode.

Besides the reduction of the expenditure for electrical lines, also thefittings are reduced in size. In addition, it is to be rendered possibleby the invention to reduce the expenditure for the driver stage of theelectronic controller. A more simple arrangement of the ducts in thevalve assembly for the control as compared to that of the state of theart is to be rendered possible by the invention.

SUMMARY OF THE INVENTION

According to the invention, the objects set out are achieved in oneembodiment by an arrangement in which the closing element of the outletvalve and the closing element of the inlet valve are coupled so that inits closing position, the closing element of the outlet valve exerts aspring force on the closing element of the inlet valve, resistingopening but permitting its opening; and, in its open position, themovement opening of the closing element of the outlet valve allowsclosing movement of the closing element of the inlet.

The outlet valve is a valve, closed when deenergized (NC valve), whichis actuatable electromagnetically as such in the prior-art manner andwhich in the deenergized condition of the actuating solenoid assumes itsnormal, closed position.

It has proved to be particularly advantageous that the valve closingelements are furnished with rods and that the coupling is constituted bya coupling housing, which is coupled to the rod of the closing elementsof the outlet valve and within which a compression coupling spring isaccommodated which exerts an expanding force on the rods of the closingelements and, thus, on the closing elements themselves.

In another embodiment, the desired control effects are achieved by abrake pressure control system having a master cylinder-pump chamberconnected to the master cylinder and the pump, a wheel cylinder chamberconnected to the wheel cylinder, and a pump suction-side chamberconnected to the suction side of the pump. An opening is providedbetween the master cylinder pump chamber and the wheel cylinder chamberwhich is closable by the inlet valve. An opening is also providedbetween the wheel cylinder chamber and the pump suction-side chamberwhich is closable by the outlet valve. Between the master cylinder pumpchamber and the wheel cylinder chamber, a restriction is providedallowing a restricted flow of fluid.

In a variation of this embodiment, two wheel chambers are provided whichare connected to each other, a first wheel cylinder chamber and themaster cylinder pump chamber isolatable by the inlet valve, and thesecond wheel cylinder chamber and the pump suction-side chamberisolatable by the outlet valve.

A further development of this concept consists in that the first wheelcylinder chamber and the pump suction-side chamber are separated by aseal, and in that the rod of the closing element of the outlet valve issealingly guided within the seal between the first wheel cylinderchamber and the pump suction-side chamber.

It is proposed with regard to the implementation of the activeconnection between the inlet valve and the outlet valve that theconnecting assembly between the rods of the inlet valve and of theoutlet valve is constituted by a coupling housing, preferably in theform of a bushing, which is coupled to the rod of the outlet valve andwhich is furnished with a stop for a front face-side collar of the rodof the inlet valve. Within the coupling housing, a compression couplingspring is positioned which acts on the bottom of the housing and on thefront face-side collar of the rod of the inlet valve which elasticallykeeps the closing element of the inlet valve and the closing element ofthe outlet valve at a determined distance variable with the distance ofthe stroke of the collar within the housing.

It may be provided in addition that the closing element of the inletvalve is arranged so as to be pre, stressed in the direction of itsvalve seat by a spring.

As further development of the invention a flow limiting valve element isprovided, comprised of a control element which is movably positionedwithin the wheel cylinder chamber and which is furnished with the inletvalve and an orifice which connect the master cylinder pump chambermaster cylinder chamber. The control element is moved by the pressuredifferential between the master cylinder pump chamber and the wheelcylinder chamber in such a way that a control edge positioned at thecontrol element passes over the cross-sectional area of the outlet portto the wheel cylinder to such an extent that a self regulating effect isachieved in the range of the cross-sectional area of the port and of thecontrol edge.

In addition, a control element comprising the inlet in the form of abushing is provided, which divides a valve chamber into a mastercylinder pump chamber and a wheel cylinder chamber. The inlet valve ismovable by the pressure differential between the master cylinder pumpchamber and the cylinder chamber, which inlet valve is furnished with anorifice having a restricted flow cross-sectional area which connects themaster cylinder pump chamber to the wheel cylinder chamber. In thepresence of a more elevated pressure in the master cylinder pumpchamber, the control element is disposed so as to be movable, againstthe force of a control spring, in the direction of the cross-sectionalarea of the outlet port. The control element is furnished with a controledge which is capable of passing at least partly over thecross-sectional area of the outlet port. The flow cross-sectional areaof the orifice, the position of the control edge with respect to thecross-sectional area of the port, the spring characteristic of thecontrol spring, the size and shape of the cross-sectional area of theport are configured such that by a self regulating process which iscaused by movement of the control edge over the port, a flow limitingeffect is attained for the wheel cylinder which leads to a determinedpressure rebuilding-up gradient within the wheel cylinder in theanti-locking control mode.

In a further preferred embodiment, it is envisaged that the controlelement in the form of a bushing divides a valve chamber into a mastercylinder pump chamber and a wheel cylinder chamber, which controlelement is movable by the pressure differential between the mastercylinder pump chamber and the wheel cylinder chamber. An orifice isprovided having a flow cross-sectional area which connects the mastercylinder pump chamber to the wheel cylinder chamber. In the presence ofa more elevated pressure within the master cylinder pump chamber, thecontrol element is disposed so as to be movable against the force of thecontrol spring in the direction of the cross-sectional area of theoutlet port to the wheel cylinder. In the normal braking mode, thecontrol element is slid by the more elevated pressure within the mastercylinder pump chamber against the force of the control spring andexpress fluid into the wheel cylinder.

In a particularly inexpensive design version, the movable controlelement is configured in the shape of a bushing with an external annulargroove, and in that an edge which comes about due to the annular groovecarries out the self regulating process as a control edge, jointly withthe cross-sectional area of the port to the supply side of the pumpand/or of the master cylinder.

By the invention, the cost of manufacture is reduced substantially. Theexpenditure for the electrical components and lines, in particular theexpenditure for magnet coils, plug pins and for the driver stage withinthe electronic controller, are considerably reduced. The assembly spacefor the control components is smaller as compared to the state of theart. The brake pressure control apparatus may be integrated in theexisting valve block of the control unit.

In alternate design variations the set-up and manufacture of the brakepressure control systems are cheaper. In particular, the expenditure forthe cable harness is substantially reduced. The plug contacts at theelectronic controller and at the pressure modulator are fewer. Also theelectronic controller itself is cheaper in its set-up and itsmanufacture by saving valve driver components. The invention allows theuse of nonpulsed inlet valves. Non pulsed inlet valves are sturdier,simpler and may be manufactured at lower cost than pulsed inlet valves.

Valve blocks equipped with the inventive brake pressure controlapparatus can be manufactured and assembled on existing facilities.

According to yet another embodiment of the invention, an inlet valve forthe wheel cylinder is provided comprised of an inlet solenoid valve andan orifice. In the normal braking mode the inlet solenoid valve isdeenergized and open, and in the control mode the inlet solenoid valveis switched by energization in a first control phase, to a closedposition. In a second control phase the inlet solenoid valve acts as anon-return valve under the action of the master cylinder pressure and/orof the pump pressure and is maintained in the closed position even ifand when the actuating solenoid is in the de-energized condition. In theclosed condition of the inlet solenoid valve fluid is conveyedrestrictedly through the orifice to the wheel cylinder. In addition tothe inlet solenoid valve, an electromagnetically controllable outletvalve is provided for the wheel cylinder, which is in the closedcondition when deenergization, which is being switched into the openposition in the control in order to bring about pressure decreaseswithin the wheel cylinder. A common electrical control line is used forboth the inlet solenoid valve and the outlet valve.

The need for a prior-art inlet valve which is open when deenergized, andthe separate line and driver components necessary for the switching ofthe inlet valve are thus eliminated.

Further details of the invention, of the objects set and of theadvantages attained are revealed by the undermentioned description ofembodiments of the invention.

DESCRIPTION OF THE DRAWINGS

Each of the FIGS. 1, 2, 4, 5 and 7 are partially sectional andfragmentary views of a combined inlet and outlet valve and schematicdepiction of other components of respective different embodiments of thesystem according to the invention.

FIG. 3 is an enlarged sectional view of a detail pertaining to theembodiments of the invention according to FIGS. 1 and 2.

FIG. 6 is a partially sectional fragmentary view of a combinedinlet-outlet valve according to a variant of the embodiments shown inFIGS. 4 and 5.

FIG. 8 shows a hydraulic circuit diagram and a partially sectional viewof two solenoid valve assemblies according to another embodiment of theinvention.

DETAILED DESCRIPTION

The descriptions and the Figures of the above cited references may bereferred to for an explanation of the background of the invention whichwill be described in the following.

In FIGS. 1 and 2 two embodiments of a combination inlet and outlet valvein a single valve housing H are illustrated. The outlet valve 10 isclosed when deenergized, the inlet valve 11 actuated by the outletvalve. The detailed description of the embodiments according to FIGS. 1and 2 can serve to complete the understanding of the embodimentsaccording to FIGS. 4 and 7.

In FIGS. 1 and 2, the brake pressure control system includes a mastercylinder 1, a wheel cylinder 2, and a motor driven pump 3. The outletvalve 10 is comprised of the upper part of the partially sectionalstructure, and includes magnet coil 4. The closing element 5 of theoutlet valve is ball-shaped and the inlet valve 11 is comprised of thelower part of the structure and includes a ball shaped closing element6. The system includes a low-pressure accumulator 7.

In FIGS. 1 and 2 the closing element 5 of the outlet valve 10 isactuated by a tie rod 8. When the magnet coil 4 is energized, the tierod 8 pulls the closing element 5 upward and will open the valve seat 9of the outlet valve 10.

The valve seat 9 of the outlet valve is located in an intermediate plate90.

A coupling between the closing element 5 of the outlet valve 10 and theclosing element 6 of the inlet valve 11 is established by rods 12, 13,and an associated coupling housing 14. Rod 12 is fixed to the couplinghousing 14 while rod 13 has a lost motion connection with head 16 ableto move away from housing bottom 17. Within the housing 14, acompression spring 15 is disposed which keeps the front face-side collar16 of the rod 13 of the closing element 6 of the inlet valve 11 inabutment against the lower stop 17 of the housing 14. In thisconfiguration, the compression spring 15 bears against the top 39 of thecoupling housing 14 and the head 16. When the closing elements of theoutlet valve 10 is against the seat 9, the spring 15 exerts a springforce resisting movement of the closing element 6 to a closed condition.

Line 18 having an orifice 19 passes by the inlet valve 11.

As is set forth above, the closing element 6 of the inlet valve 11 isindirectly actuated by the closing elements of the outlet valve 10through the rods 12, 13 and housing 14.

In the normal braking mode, fluid will flow through the line 20 into achamber 21 in the valve housing H connected to the master cylinder 1 andthe outlet of the pump 3 by actuation of the master cylinder 1. In thissituation, the inlet valve 11 is held open by the force of spring 15.Fluid will flow thence into an intermediate chamber 22 connected to thewheel cylinder 2. From there, fluid flows through the line 23 into thewheel cylinder 2.

In the anti-locking control mode, the pump 3 will be put into operationby starting of the electric driving motor as commanded by an outputcommand signal of the electronic controller.

In addition, the magnet coil 4 will be energized by a further outputsignal of the controller. By the action of the tie rod 8, the closingelement 5 of the outlet valve will be lifted and, thus, open the seat 9of the outlet valve 10.

Simultaneously, the seat 24 of the inlet valve 11 will be closed by theclosing element 6 due to the described coupling between the closingelement 5 of the outlet valve 10 and the closing element 6 of the inletvalve 11 15 and rod 13. The closing element 6 of the inlet is subject tothe force of a compression spring 25 to be urged closed.

The direct fluid connection between the master cylinder 1 and the wheelcylinder 2 is, thus, interrupted. The pump 3 will deliver fluid underpressure through the line 58 into the chamber 21.

Fluid is allowed to flow into the wheel cylinder chamber 22 onlyrestrictedly through the orifice 19. In this situation, more fluid willflow through the valve seat 9 of the outlet valve 10 out of theintermediate chamber 22 into a pump suction-side connected chamber 27than fluid flowing into the intermediate wheel cylinder chamber 22through the orifice 19.

The pump suction-side chamber 27 is connected through the line 28 to thesuction side of the pump 3. A branch line 29 connects the suction line28 to the low-pressure accumulator 7.

In the embodiment according to FIG. 2, the pump suction-side chamber 34is located between an inter-mediate plate 91 which incorporates thevalve seat 9 of the outlet valve 10, on one side, and an intermediateplate 94, on the other side. The intermediate plate 94 is furnished witha seal which guides the rod 12.

In the embodiment according to FIG. 2, two wheel cylinder connectedchambers exist, namely a first wheel cylinder chamber 30 and a secondwheel cylinder chamber 31. The first wheel cylinder chamber 30 isconnectable through the inlet valve 11 to the master cylinder pumpchamber 21. The second wheel cylinder chamber 31, linked to the firstwheel cylinder chamber 30 through the line 32, is disposed upstream ofthe outlet valve 10 with respect to the flow direction. In theembodiment according to FIG. 2, the closing element 5 of the outletvalve 10 is, thus, subjected to the wheel cylinder pressure in thenormal braking mode. As a consequence, the closing element 5 will bepressed onto the valve seat 9, which leads to a better sealing. Thevalve seat 9 is located in intermediate plate 91.

In the event of actuation of the master cylinder 1 which is furnishedwith the fluid reservoir 26, brake fluid will be conveyed into themaster cylinder pump chamber 21 through the line 20. From there, thebrake fluid reaches the first wheel cylinder chamber 30 and over theline 23 the wheel cylinder 2. At the same time, fluid will flow over theline 32 into the second wheel cylinder chamber 31.

In the anti-locking control mode, the pump 3 starts and the magnet coil4 is energized. The closing element 5 is lifted and will open up valveseat 9 of the outlet valve 10. The closing element 6 of the inlet valvecloses.

Flow from the pump 3 thus enters chamber 21 only through the orifice 19.As a result, only a slight volume of fluid will flow through the orifice19 into the first wheel cylinder chamber 30. A larger volume of fluidwill flow out of the second wheel cylinder chamber 31 through the openoutlet valve into the pump suctionside chamber 34, and through the line28 to the suction side of the pump 3.

A pressure decrease within the wheel cylinder 2 will thus occur.

In FIG. 3, it can be seen that the valve seat 36 of the inlet valve 11is alternatively formed with a notch 37. The notch 37 acts as arestrictor opening or orifice when the closing element 6 of the inletvalve comes to rest on the valve seat 36. Reference numeral 38 denotesthe main area of opening of the inlet valve seat 36.

In a corresponding manner, a notch restrictor opening may be provided inthe closing element 6 of the inlet valve 11 as a further alternative.

A separate line with an orifice, which bypasses the inlet valve 11 maybe eliminated by using the restrictor openings in the closing element 6or in the valve seat 36.

In FIG. 4, fluid will be delivered by the master cylinder 1 over theline 33 into the master cylinder pump chamber 35 in the normal brakingmode. The inlet valve 11 being open, fluid will be conveyed into thefirst wheel cylinder chamber 40 and from there through the port 41 ofthe line 42 forth to the wheel cylinder 2. Through the line 43, thesecond wheel cylinder chamber 44 is filled with fluid.

In the anti-locking control mode, the pump 3 will be put into operationand the inlet valve 11 will be closed, closing element 6 coming to reston the valve seat.

The pump 3 delivers fluid under pressure into the master cylinder pumpchamber 35 via line 59. The pump 7 pressure is exerted against the lowerfront wall of a control bushing 48 and on one side of an orifice 49 inthe bushing 48. As a consequence, the control bushing 48 moves in anupward direction as viewed in FIG. 4. The orifice 49 allows only aslight volumetric flow.

Simultaneously, the outlet valve 10 is opened, and, closing element 5will be lifted off from the valve seat in the intermediate plate 92. Thevalve seat 9 is thus opened.

Fluid will now be allowed to flow out of the wheel cylinder 2 throughthe line 43 the second wheel cylinder chamber 44, and into the pumpsuction-side chamber 45. The pump suction-side chamber 45 is separatedwith respect to the first wheel cylinder chamber 40 by an intermediateplate 76 with seal. The pump suction-side chamber 45 is connectedthrough the line 46 to the suction side of the pump 3. The line 46 isequipped with an orifice 47 and is connected to the low-pressureaccumulator 7.

The flow cross-sectional area of the orifice 49 located in the bottom ofthe control bushing 48, the position of the control edge 50 of thecontrol bushing 48, the characteristics of the control spring 51, thesize and the shape of the cross-sectional area of the port 41 to theline 42 leading to the wheel cylinder 2 have parameters and areconfigured such that the control edge 50 passes over part of thecross-sectional area of the port 41 A self-thereby established. Thismeans that on reaching a nominal flow rate (volume of fluid per unit oftime) a substantially constant flow of fluid will be conveyed to thewheel cylinder 2, no matter what the pressure level of the pump pressureand/or of the master cylinder is.

A stop 52 positions the control bushing 48 in its position of rest.

In the embodiment according to FIG. 5, a simplification has been carriedout with respect to the previously described embodiments.

In the embodiment according to FIG. 5 the customary inlet valve withclosing element and valve seat is eliminated. The master cylinder pumpchamber 53 is separated from the first wheel cylinder chamber 54 by acontrol bushing 55 which is prestressed by a control spring 95. Aconnection between the master cylinder pump chamber 53 and the wheelcylinder chamber 54 exists solely due to the orifice 56 in the bottom ofthe control bushing 55.

In the normal braking mode, the master cylinder 1 delivers fluid throughthe line 57 into the master cylinder pump chamber 53. The controlbushing will be slid in upward direction due to the pressure which isbuilt up within the master cylinder pump chamber 53.

In this manner, fluid will be expressed out of the first wheel cylinderchamber 54 which is closed by the plate 60 into the wheel cylinder 2through the line 61.

In the anti-locking control mode, the operation of the pump 3 isinitiated and delivers fluid through the line 67 into the mastercylinder pump chamber 53. The outlet valve is also opened at the sametime.

Fluid flows through line 62 from the wheel cylinder 2 into the secondwheel cylinder chamber 63 and from there through the opened outlet valve10 into pump suction side chamber 64. Fluid is delivered over the line65 from the pump suction side chamber 64 to the suction side of the pump3. Also in this instance, the line 65 is furnished with an orifice 66.The line 65 is connected to the low-pressure accumulator.

In the anti-locking control mode, the control bushing 55 is slid furtherupward due to the pump pressure in the master cylinder pump chamber 53,so that the control edge 68 of said control bushing 55 jointly with thecross-sectional area of the port to the line 61 going to the wheelcylinder 2 will carry out a self regulating process similarly as hasbeen described in connection with FIG. 4.

Also, in the embodiment according to FIG. 5, the spring characteristicof the control spring, the axial extension of the control spring, theposition of the control bushing 55 and the control edge, 68, the sizeand the shape of the port 69 to the supply line 61 going to the wheelcylinder 2, and the cross-sectional flow area of the orifice 56 in thebottom of the control bushing 55, have to be set with one another insuch a way that the desired self regulating effect comes about in therange of the cross-sectional area of the port 69 of the line going tothe wheel cylinder 2.

In this embodiment, too, the effect of a flow limiting valve as has beendescribed above will be achieved due to the self regulating effect.

FIG. 6 shows an alternative of the coupled inlet-outlet valve as perFIG. 1. A physical separation exists between the closing element 6 ofthe inlet valve 11 and the rod 70.

At its upper end, a rod 70 is provided with a bushing 71 which isfurnished with a stop 72. The rod 73 projects into the bushing 71, whichis coupled to the closing element 5 of the outlet valve 10. The rod 73is guided in the intermediate plate 93 by a seal. At its lower end, therod bears a collar 74 which in the event of opening of the outlet valve10, that is to say, when the valve element 5 is lifted up, this willpull the rod 70 in an upward direction through the stop 72 and thebushing 71. A compression spring 96 is positioned between the bottom ofthe housing 71 and the collar 74.

The closing element 6 of the inlet valve 11 is subject to the pressureof the spring 75 which will urge the closing element 6 of the inletvalve against the valve seat of the inlet valve 11 when the outlet isopen, that is to say, when the rod 70 has been pulled upward.

That means that as to its effect, in this embodiment there is an inverserelation as compared to the coupling as per FIGS. 1 to 5. In FIGS. 1 to5, see, for example, FIG. 4, the closing element of the inlet valve 11is rigidly coupled to the rod.

In the embodiment according to FIG. 7, a coupling is envisaged betweenthe closing element 5 of the outlet valve 10 and the closing element 6of the inlet valve as has been described in reference to FIG. 1.

The differences of the embodiment according to FIG. 7 consists in thatan intermediate plate with seal as is denoted by reference numeral 76 inFIG. 4 is eliminated in FIG. 7.

In the normal braking mode, the master cylinder 1 will deliver fluidthrough the line 89 into the master cylinder pump chamber 77.

Fluid will be conveyed through the opened inlet valve 11 into the wheelcylinder chamber 78. From there, fluid will be delivered over the line79 to the wheel cylinder 2.

In the anti-locking control mode the pump 3 is put into operation. Itdelivers fluid via line 80 into the master cylinder pump chamber 77.

As described above, the inlet valve 11 is closed and outlet 10 is openedin the control mode. Fluid can be conveyed out of the wheel cylinder 2over the line 79, through the wheel cylinder chamber 78, through theflow cross-sectional area 9 of the outlet valve, through the pumpsuction-side chamber 81, through the line 82 to the suction side of thepump 3.

Simultaneously, pressure will be built up by the pump 3 in the mastercylinder pump chamber 77 which is higher than the pressure in the wheelcylinder chamber 78. Due to the pressure differential which is sogenerated, the bushing 83 which is furnished with an extension 84 andwith a control edge 85 will move upward. The control edge 85 is formedby an annular groove 97 in the extension 84. Due to the upward motion ofthe bushing 83, the control edge 85 of the extension 84 enters the rangeof the cross-sectional area of the port 86 to the supply line of thepump 3 and of the master cylinder 1.

A self regulating effect comes about in this situation. The position ofthe control edge 85, the shape, the size and the position of thecross-sectional area of the port 86, the characteristic of the spring87, the flow cross-sectional area of the orifice 88 which is positionedat the bottom of the bushing 83 are set with one another in such a waythat the effect of a flow limiting valve which has been described beforeis brought about.

FIG. 8 shows the hydraulic circuit diagram and two solenoid valveassemblies according to the invention.

In FIG. 8, a master cylinder 1 is furnished with fluid from a reservoir102. A pump 3 is put into operation in the control mode by a startingsignal of the controller (not shown), which starts the driving motor ofthe pump. A line 104 leads to the wheel cylinder of one brake.

Two valve assemblies are visible in FIG. 8, an inlet solenoid valve 105and an outlet valve 106.

As distinguished from the state of art, the inlet solenoid valveassembly 105 is not configurated as a standard valve, open whendeenergized (NO valve). Rather the inlet solenoid valve 105 can performthe function of a non-return valve.

The outlet valve assembly 106 is configured as a valve closed whendeenergized (NC valve).

In FIG. 8, the inlet solenoid valve 105 and the outlet valve assembly106 are shown in the closed condition. That means that the closingelement 6 of the inlet solenoid valve 105 rests on the valve seat 114,and the closing element 5 of the outlet valve assembly 106 rests on thevalve seat 116.

In the normal braking mode, fluid is delivered by the master cylinder 1over the line 20 into the chamber 108. In the normal braking mode, theinlet solenoid valve 105 is deenergized and open. Fluid is thus conveyedto the wheel cylinder through the open cross-sectional area 109 andthrough the ducts 110, 111. The delivery direction to the wheel issymbolized by the arrow 112.

In the anti-locking control mode, the coil 123 of the solenoid of theinlet solenoid valve 105 will be energized.

The closing element 6 will move downward and will close the valve seat114. This is the situation which is illustrated in FIG. 8. As a result,the direct flow connection of the fluid between the duct 117 and theduct 110 will be interrupted.

Fluid will be conveyed through the annular passages 118, 119 and throughthe chamber 122 in the inlet solenoid valve assembly 105 to the rearside 121 of the rod 120 bearing the closing element 6 and, thus, ontothe cross-sectional area of the closing element 6, which is effective asto pressure, and will press the latter onto the valve seat.

In this situation, the inlet solenoid valve 105 acts as a non-returnvalve 105.

That means that in the control mode the closing element 6 will bepressed onto the valve seat 114 by the master cylinder pressure and/orby the pressure of the pump also if and when the coil 123 is in thedeenergized condition.

This results in the important advantage that the coil 124 of the outletvalve 100, closed when deenergized, may be controlled in accordance withthe control algorithm through one line only for both coils 123,124,without the closed condition of the inlet solenoid valve/non-returnvalve 105 being thereby canceled.

If at the beginning of the control mode, there has been an initialenergization of the coil 123 of the inlet solenoid valve 105, the valve105 remains open no matter whether the energization of the coil 123continues or is interrupted.

In the anti-locking control mode, fluid will restrictedly flow throughthe orifice 19 into the duct 111 when the non-return inlet valve 105 isin the closed condition.

For the purpose of a pressure reduction in the wheel cylinder in theanti-locking control mode, the valve 106, closed when deenergized, willbe opened after the inlet solenoid valve 105 acting as a non-returnvalve has been closed.

In particular, by the energization of the coil 124 of the outlet valve106, closed when deenergized, the valve seat 126 is opened due to theclosing element 5 being lifted upward. As a result, fluid may beconveyed through the line 128 in the direction of the arrow 127 out ofthe wheel cylinder to the suction side of the pump 3. Reference numeral7 denotes a damping unit which comprises a low-pressure accumulator.

In order to bring about a pressure rebuilding-up phase in the wheelcylinder during the control mode, the outlet valve 106, is closed whendeenergized, is closed by interrupting the current supply to the magnetcoil 124. As illustrated above, it is without importance that due to thecommon electric line also the magnet coil 123 of the inlet solenoidvalve 105 is no longer energized, but the master cylinder pressureand/or the pump pressure will maintain the non-return valve 105 in itsclosed position as has been described above.

The common electric line 130 can be seen in FIG. 8. In this embodimentthere is, a parallel connection of the coils 123 and 124. As mentionedin the beginning, the two coils may also be connected in series as well.

The invention is applicable for so-called open hydraulic systems or forclosed systems.

In an open system, the hydraulic line 131 illustrated as a dashed lineexists, which forms a connection to the fluid reservoir 102 being openwith respect to the atmosphere.

The closed system is constituted by the lines 132, 133. Fluid isconveyed by the pump 3 directly into the supply line 20 between themaster cylinder 1 and the inlet solenoid valve/non-return valve 105.

Further embodiments can be imagined for the realization of the basicthought of the invention. For example, it is possible to achieve theorifice function in that a recess is provided in the closing element 6of the inlet solenoid valve, which acts the way of an orifice or of arestrictor.

In the same manner, a recess may be provided in the valve seat 114 ofthe inlet solenoid valve, which presents a small flow cross-sectionalarea and which, too, brings about an orifice effect in this way.

Summarizing the above, it can be said that by the present invention theconventional valve, open when deenergized, is replaced, as far as itseffect is concerned, by a magnetically pilotable non-return valve, anorifice bypass in the non-return valve.

As an alternative of the forementioned design, the orifice may beconnected in parallel. The magnet coils of the valve, closed whendeenergized, and of the inlet solenoid valve acting as a non-returnvalve are, advantageously, controlled through a common line by onedriver stage only of the electronic controller. The electrical circuitsof the solenoid are designed such that the inlet solenoid valve whichperforms the function of a non-return valve closes before, closed whendeenergized, opens. Now, once the inlet solenoid valve with itsnon-return valve function is closed, it will remain closed also withoutenergization of the coil, and for that matter, as long as the mastercylinder pressure and/or the pump pressure is higher than the pressurein the wheel cylinder.

We claim:
 1. A brake system for automotive vehicles including a wheelbrake, a master cylinder, and a wheel cylinder for said wheel brake,said master cylinder able to generate hydraulic fluid pressure tooperate said wheel cylinder, a brake pressure control system includingat least one motor-driven pump for the generation of a hydraulic fluidpressure to operate said wheel cylinder and said brake pressure controlsystem, said pump having a suction and a pressure side, an electroniccontroller, an inlet valve which is associated with said wheel cylinderto control fluid communication of said wheel cylinder with said mastercylinder and said pump, and an outlet valve controlling communication ofsaid wheel cylinder with a low pressure region of said controlsystem;wherein said outlet valve includes a closing element operated bysaid electronic controller, said closing element movable between aclosed position closing communication through said outlet valve and anopen position opening communication through said outlet valve, saidinlet valve also including a closing element movable between a closedposition closing communication through said inlet valve and an openposition opening communication through said inlet valve, biasing meansbiasing said inlet valve closing element toward said closed position,said respective closing elements coupled to each other through couplingmeans, said coupling means including means causing said closing elementof said outlet valve when in said closed position to exert a springforce on said closing element of said inlet valve resisting movementthereof to said closed position, said coupling means further includingmeans operative upon movement of said closing element of said outletvalve to said open position allowing free closing movement of saidclosing element of said inlet valve induced by said biasing means.
 2. Abrake system as claimed in claim 1, wherein said outlet valve is asolenoid operated valve, closed when deenergized.
 3. A brake system asclaimed in claim 1, wherein said outlet valve includes a rod movablewith said outlet valve closing element and said inlet valve includes arod movable with said inlet valve closing element; wherein said couplingmeans is constituted by a coupling housing receiving at either end arespective one of said rods in opposing fashion, one of said rods fixedto said coupling housing, the other rod having a lost motion connectionable to move into said coupling housing; and, a compression springaccommodated in said coupling housing which exerts a spreading force onsaid rods.
 4. A brake system as claimed in claim 3, wherein said brakepressure control system further includes a valve housing receiving bothsaid inlet and outlet valves, a master cylinder pump chamber defined insaid valve housing connected to said master cylinder and said pump, saidbrake pressure control system also including a wheel cylinder chamberdefined in said valve housing connected to said wheel cylinder, saidbrake pressure control system further including a pump suction-sidechamber defined in said valve housing connected to said suction side ofsaid pump an opening being provided between said master cylinder pumpchamber and said wheel cylinder chamber closable by said inlet valve, anopening provided between said wheel cylinder chamber and said pumpsuction-side chamber closable by said outlet valve, a flow restrictingpassage between said master cylinder pump chamber and said wheelcylinder chamber allowing restricted flow therebetween in the closedcondition of said inlet valve.
 5. A brake system as claimed in claim 4,wherein a first wheel cylinder chamber and a second wheel cylinderchamber are defined in said valve housing, which each have a fluidcommunication with each other, said first wheel cylinder chamber andsaid master cylinder pump chamber isolatable by said inlet valve, saidsecond wheel cylinder chamber and said pump suction-side chamberisolatable by said outlet valve.
 6. A brake system as claimed in claim5, wherein said first wheel cylinder chamber and said pump suction-sidechamber are separated by an intermediate plate with a seal, and whereinsaid rod of said closing element of said outlet valve is guided withinsaid seal of said intermediate plate.
 7. A brake system as claimed inclaim 4, wherein said inlet valve includes a valve seat cooperating withsaid inlet valve closing element to control communication through saidinlet valve and wherein said restricting passage comprises a notch inone of said valve seat or said inlet valve closing element, allowingrestricted fluid flow with said inlet valve closing element on saidinlet valve valve seat.
 8. A brake system as claimed in claim 1, whereinsaid inlet valve includes a valve seat cooperating with said inlet valveclosing element to control opening and closing of said inlet valve, aspring engaging said inlet valve closing element and wherein said inletvalve closing element is prestressed in the direction of said inletvalve valve seat by said spring.
 9. A brake system as claimed in claim 4further including flow limiting valve means limiting flow from saidwheel cylinder chamber to said wheel cylinder, said flow limiting valvemeans including a control element movably positioned within said wheelcylinder chamber and subject to fluid pressure in said master cylinderpump chamber, a spring acting to resist movement of said control elementcaused by fluid pressure in said master cylinder pump chamber, saidmovable element having an opening controlled by said inlet valve, andalso having an orifice connecting said master cylinder pump chamber tosaid wheel cylinder chamber comprising said restricting passage, a portin said valve housing communicating said wheel cylinder with said wheelcylinder chamber, said control element having a control edge moved by apressure differential between said master cylinder pump chamber and saidwheel cylinder chamber so that said control edge passes over said portand a self regulating effect is achieved by movement of said controledge over said port.
 10. A brake system apparatus as claimed in claim 4,wherein said control element is interposed between said master cylinderpump chamber and said wheel cylinder chamber and is movable by apressure differential between said master pump chamber and said wheelcylinder chamber, said control element having an orifice formed therein,said orifice having a restricted flow cross-sectional area connectingsaid master cylinder pump chamber and said wheel cylinder chamber tocomprise said flow restricting passage, a control spring in said mastercylinder pump chamber acting on said flow limitation control element sothat upon development of a higher pressure in said master cylinder pumpchamber than said wheel cylinder chamber said control element movesagainst the force of said control spring; a port in said valve housingopening to said master cylinder and said pump pressure side, saidcontrol element formed with a control edge capable of passing at leastpartly over said port, the cross-sectional area of said orifice, theposition of said control edge with respect to said port, thecharacteristics of said control spring, the size and the shape of saidcross-sectional area of the port configured such that a self regulatingprocess is caused by movement of said control edge over said port and aflow limiting effect is attained for flow from said pump to said mastercylinder pump chamber, whereby a predetermined pressure rebuilding-upgradient is achieved within said wheel cylinder by said pump.
 11. Abrake system as claimed in claim 9, wherein said movable control elementhas an external annular groove forming said control edge.